.overlay-mask {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background-color: rgba(0, 0, 0, 0.5);
    z-index: 1000;
    display: none;
    justify-content: center;
    align-items: center;
}

.loader {
    border: 5px solid #f3f3f3; /* Light grey */
    border-top: 5px solid #3498db; /* Blue */
    border-radius: 50%;
    width: 50px;
    height: 50px;
    animation: spin 2s linear infinite;

    /* 相对于body定位 */
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);  /* 精确居中 */
}

@keyframes spin {
    0% { transform: rotate(0deg); }
    100% { transform: rotate(360deg); }
}